CVE-2003-0971 in GnuPG
Summary
by MITRE
GnuPG (GPG) 1.0.2, and other versions up to 1.2.3, creates ElGamal type 20 (sign+encrypt) keys using the same key component for encryption as for signing, which allows attackers to determine the private key from a signature.
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Analysis
by VulDB Data Team • 12/15/2024
The vulnerability described in CVE-2003-0971 represents a critical cryptographic flaw in GnuPG versions 1.0.2 through 1.2.3 that fundamentally undermines the security of ElGamal type 20 keys. This issue falls under the category of cryptographic weakness where the implementation fails to properly separate encryption and signing components, creating a dangerous overlap in key material. The vulnerability specifically affects ElGamal keys with type 20, which are designed to provide both digital signature and encryption capabilities, but the flawed implementation uses identical key components for both operations.
The technical flaw stems from a fundamental design error in how GnuPG generates ElGamal keys for type 20 operations. When creating these hybrid keys, the system incorrectly employs the same mathematical components for both encryption and signing functions, violating core cryptographic principles that require distinct key material for different operations. This particular implementation error creates a mathematical vulnerability where the private key can be derived from a single signature, effectively breaking the security model that relies on the computational difficulty of deriving private keys from public information. The flaw operates at the mathematical level, specifically exploiting the relationship between the discrete logarithm problem and the shared key components between encryption and signature operations.
The operational impact of this vulnerability is severe and far-reaching for any system utilizing affected GnuPG versions. Attackers who can obtain a single signature created with a vulnerable ElGamal type 20 key can immediately compute the corresponding private key, rendering all encryption and digital signature capabilities based on that key pair completely compromised. This vulnerability affects the integrity of digital signatures, as the private key can be recovered and used to forge signatures, and it simultaneously compromises the confidentiality of encrypted communications since the private key can be used to decrypt messages. The attack vector is particularly dangerous because it requires minimal resources and can be executed by anyone with access to a single signature, making it a significant threat to organizations relying on GnuPG for security. This vulnerability directly relates to CWE-327, which addresses weak cryptographic algorithms and improper key management, and aligns with ATT&CK technique T1552.004 for unsecured credentials and T1552.006 for data manipulation.
The mitigation strategy for this vulnerability involves immediate upgrading to GnuPG versions that properly implement ElGamal key generation, specifically versions 1.2.4 and later where the implementation was corrected. Organizations must revoke and regenerate all ElGamal type 20 keys that were created using vulnerable versions, ensuring that new keys use distinct components for encryption and signing operations. System administrators should conduct comprehensive audits of key usage and implement proper key lifecycle management practices to prevent similar issues in the future. The corrected implementation ensures that encryption and signing operations utilize independent mathematical components, thereby maintaining the security properties necessary for both cryptographic functions. Security teams must also consider the broader implications of key compromise and implement monitoring systems to detect potential misuse of previously compromised keys, while following industry best practices for key management and cryptographic implementation as outlined in standards such as NIST SP 800-57 for key management and ISO/IEC 14443 for cryptographic security requirements.